An-Nisa 4:25 ومن لم يستطع منكم طولا ان ينكح المحصنات المومنات فمن ما ملكت ايمانكم من فتياتكم المومنات والله اعلم بايمانكم بعضكم من بعض فانكحوهن باذن اهلهن واتوهن اجورهن بالمعروف محصنات غير مسافحات ولا متخذات اخدان فاذا احصن فان اتين بفاحشة فعليهن نصف ما على المحصنات من العذاب ذالك لمن خشي العنت منكم وان تصبروا خير لكم والله غفور رحيم ٢٥

If one cannot afford to marry the free Muslim women, then (he may marry) the one you people own of your Muslim girls. Allah knows best about your faith. You are similar to each other.So, marry them with the permission of their masters, and give them their dues, as recognized, they being bound in marriage, not going for lust, nor having paramours. So, once they have been bound in marriage, then, if they commit a shameful act, they shall be liable to half of the punishment prescribed for the free women. That is for those of you who apprehend to indulge in sin. But that you be patient is better for you. Allah is Most-Forgiving, Very-Merciful.